Gallium Nitride-Based III-V Group Compound Semiconductor Device and Method of Manufacturing the Same

ABSTRACT

The present invention relates to a gallium nitride-based compound semiconductor device and a method of manufacturing the same. According to the present invention, there is provided a gallium nitride-based III-V group compound semiconductor device comprising a gallium nitride-based semiconductor layer and an ohmic electrode layer formed on the gallium nitride-based semiconductor layer. The ohmic electrode layer comprises a contact metal layer, a reflective metal layer, and a diffusion barrier layer.

TECHNICAL FIELD

The present invention relates to a gallium nitride-based compoundsemiconductor device and a method of manufacturing the same, and moreparticularly, to a gallium nitride-based III-V group compoundsemiconductor device having an Me (=Ir, Ni, Pt)/Ag/Ru/Ni/Au ohmicelectrode having low contact resistivity, high reflectance, and goodthermal stability and a method of manufacturing the same.

BACKGROUND ART

Recently, light emitting diodes (LEDs) using a gallium nitride-basedsemi-conductor (hereinafter, referred to as GaN LEDs) have been expectedto be substituted for conventional light sources such as incandescentlamps, fluorescent lamps, and mercury lamps. Therefore, active researchhas been done on high-power GaN LEDs. In general, since a GaN LED filmlayer is grown on a sapphire substrate that is an insulator, theassociated LED device has a horizontal structure. As a result, theconventional LED device has disadvantageously a high operation voltageand a low light output because current spreading resistance increasesduring a high power operation thereof. In addition, the conventional LEDdevice has also disadvantageously poor thermal stability because heatgenerated during the operation thereof cannot be efficiently dissipatedfrom the sapphire substrate.

In order to solve the aforementioned problems, a flip-hip packagingmethod has been proposed to implement a high-power GaN LED. Since lightemits upwards through the sapphire substrate from an active layer of theGaN LED having a flip-chip structure, a thick p-type ohmic electrode canbe substituted for a transparent electrode, so that the currentspreading resistance can be reduced. At this time, a materialconstituting the p-type ohmic electrode should have low absorbance andhigh reflectance. Since metals such as Ag and Al having a reflectance of90% or more have a low work function, these metals are not suitable forcontact metals of the p-type GaN ohmic electrode. On the other hand,with respect to an InGaN LED device, research has rarely been done on ahigh-reflectance p-type ohmic electrode in comparison to a conventionalp-type transparent electrode.

A recent research shows that, an Ni/Au transparent electrode on which Aland Ag reflective layers are deposited can have a reflectance of 70% ormore in a blue light range (see Appl. Phys. Lett. vol. 83, p. 311(2003)). However, there is a problem in that properties of theelectrodes drastically deteriorate at a temperature of 100° C. or more.

DISCLOSURE OF INVENTION Technical Problem

The present invention is conceived to solve the aforementioned problemsin the prior art. Accordingly, an object of the present invention is toprovide a gallium nitride-based III-V group compound semiconductordevice and a method of manufacturing the same capable of improvingperformance of the device by forming an ohmic electrode having goodthermal stability, improved contact resistivity, and highly-maximizedreflectance.

Technical Solution

According to an aspect of the present invention for achieving theobjects, there is provided a gallium nitride-based III-V group compoundsemiconductor device. The semiconductor device comprises a galliumnitride-based semiconductor layer and an ohmic electrode layer formed onthe gallium nitride-based semiconductor layer. The ohmic electrode layercomprises a contact metal layer, a reflective metal layer, and adiffusion barrier layer.

The ohmic electrode layer may further comprise at least one bondingmetal layer. The ohmic electrode layer may be formed by sequentiallylaminating the contact metal layer, the reflective metal layer, thediffusion barrier layer, and the bonding metal layer. The contact metallayer may comprise at least one of Ni, Ir, Pt, Pd, Au, Ti, Ru, W, Ta, V,Co, Os, Re, and Rh. The reflective metal layer may comprise at least oneof Al and Ag. The diffusion barrier layer may comprise at least one ofRu, Ir, Re, Rh, Os, V, Ta, W, ITO (Indium Tin Oxide), IZO (Indium Zincoxide), RuO₂, VO₂, MgO, IrO₂, ReO₂, RhO₂, OsO₂, Ta₂O₃, and WO₂. Thebonding metal layer may comprise first and second bonding metal layers,said first bonding metal layer comprising at least one of Ni, Cr, Ti,Pd, Ru, Ir, Rh, Re, Os, V, and Ta, said second bonding metal layercomprising at least one of Au, Pd, and Pt.

According to another aspect of the present invention for achieving theobjects, there is provided a method of manufacturing a galliumnitride-based III-V group compound semiconductor device. The methodcomprises steps of: forming a gallium nitride-based semiconductor layerhaving a PN contact structure on a substrate; and forming an ohmicelectrode layer on the semiconductor layer. The ohmic electrode layercomprises a contact metal layer, a reflective metal layer, and adiffusion barrier layer.

The step of forming the ohmic electrode layer may comprise steps of:sequentially laminating the contact metal layer, the reflective metallayer, and the diffusion barrier layer on the semiconductor layer;performing a thermal treatment process; and forming a bonding metallayer on the diffusion barrier layer. The step of forming the ohmicelectrode layer comprises steps of: sequentially laminating the contactmetal layer, the reflective metal layer, the diffusion barrier layer andbonding metal layer on the semi-conductor layer; and performing athermal treatment process. The thermal treatment process may be a rapidthermal annealing process performed under an atmosphere of 5 to 100%oxygen at a temperature of 100 to 700° C. for 10 to 100 seconds.

DESCRIPTION OF DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a schematic cross-sectional view showing a p-type ohmicelectrode of a gallium nitride-based compound semiconductor layeraccording to an embodiment of the present invention;

FIG. 2 is a graph showing current versus voltage of ohmic electrodesaccording to the present invention under different thermal treatmentatmospheres;

FIG. 3 is a graph showing contact resistivity of the ohmic electrodeaccording to the present invention and a conventional Ni/Au ohmicelectrode with respect to thermal treatment temperature;

FIG. 4 is a graph showing reflectance of the ohmic electrode accordingto the present invention and a conventional Ni/Au ohmic electrode;

FIG. 5 is a graph showing depth profiles of an ohmic electrode accordingto the present invention, wherein the depth profiles are measured byusing a secondary ion-mass spectroscopy (SIMS) with respect to thermaltreatment conditions;

FIG. 6 is a graph showing operation voltage and light output offlip-chip light emitting diodes manufactured by using an ohmic electrodeaccording to the present invention and a conventional Ni/Au ohmicelectrode;

FIG. 7 is a graph showing operation voltage of vertical-structure lightemitting diodes manufactured by using an ohmic electrode according tothe present invention and a conventional Ni/Au ohmic electrode;

FIG. 8 is a graph showing light output of the vertical-structure lightemitting diodes manufactured by using an ohmic electrode according tothe present invention and a conventional Ni/Au ohmic electrode; and

FIG. 9 is a photograph of the vertical-structure LED.

BEST MODE

Hereinafter, a gallium nitride-based compound semiconductor devicecomprising an ohmic electrode layer and a method of manufacturing thesame will be described with reference to the accompanying drawings. Theohmic electrode layer includes a reflective metal layer made of Ag, adiffusion barrier layer made of Ru, a first bonding metal layer made ofNi, and a second bonding metal layer made of Au.

FIG. 1 is a schematic cross-sectional view showing a configuration of anohmic electrode of a gallium nitride-based compound semiconductor layeraccording to an embodiment of the present invention.

Referring to FIG. 1, an n-type GaN layer 12, an active layer 13, and ap-type GaN layer 14 are sequentially formed on a substrate 11. Then, amulti-layered ohmic electrode layer is formed by sequentially depositingcontact metal/Ag/Ru/Ni/Au metal layers 15 to 19 on the p-type GaN layer14. The ohmic electrode layer has a total thickness of 300 to 23,000?,and more preferably, 2,000 to 5,000?. The contact metal layer 15 has athickness of 5 to 500?, and more preferably, 200? or less. In addition,the contact metal layer 15 may be formed as a multi-layered thin film.The Ag layer 16 has a thickness of 100 to 9,000?, and more preferably,1,000 to 2,000?. The Ru layer 17 has a thickness of 50 to 1,000?, andmore preferably, 100 to 800?. The Ni layer 18 has a thickness of 100 to3,000?, and more preferably, 1,000? or less. The Au layer 19 has athickness of 100 to 9,000?, and more preferably, 1,000? or less. Thethickness of the contact metal layer 15 is selected within theaforementioned range in order to control absorbance of light.

The contact metal layer 15 is made of one of Ni, Ir, Pt, Pd, Au, Ti, Ru,W, Ta, V, Co, Os, Re, and Rh. Alternatively, the contact metal layer 15may be formed by alternately laminating two different metals of theabove-listed metals. Preferably, the contact metal layer 15 is formed bylaminating Ni, Ir, and Pt layers.

A method of forming the multi-layered ohmic electrode layer is asfollows. Firstly, the n-type GaN layer 12, the active layer 13, and thep-type GaN layer 14 are sequentially formed on a sapphire substrate 11.Next, the p-type GaN layer 14 is subject to a mesa-etching process usinginductively coupled plasma (ICP), a surface treatment process, alithography process, a metal thin film deposition process, and alift-off process, so that a metal electrode pattern is obtained. Thesurface treatment process for the p-type GaN layer 14 is performed byimmersing the p-type GaN layer 14 in aqua regia (HCl:HNO3=3:1) for tenminutes, cleaning the resultant product with de-ionized water, anddrying the resultant product with nitrogen.

Before the metal layer is deposited, another surface treatment processis performed with a solution of HCl and de-ionized water (1:1) for oneminute. Then, in an e-beam evaporator, metal (Me=Ir, Ni, Pt)/Ag/Ru/Ni/Aulayers 15 to 19 are sequentially deposited to form an ohmic electrode.Next, the ohmic electrode is subject to a rapid thermal annealingprocess under an atmosphere of 5% or more oxygen at a temperature of 100to 700° C. for 10 or more seconds. That is, the rapid thermal annealingprocess is preferably performed under an atmosphere of 5 to 100% oxygenat a temperature of 100 to 700° C. for about 10 to 100 seconds. Next,the electrical properties of the ohmic electrode are measured, so thatcontact resistivity thereof is calculated.

More preferably, the contact metal (Me=Ir, Ni, Pt), Ag, and Ru layers 15to 17 are sequentially deposited on the p-type GaN layer 14. Then, theresultant product is subject to a thermal treatment process under anoxygen atmosphere. Since the Ru layer 17 serves as a diffusion barrierlayer formed on the Ag layer 16 which serves as a reflective layer, itis possible to prevent diffusion and oxidation of Ag in the Ag layer 16during the thermal treatment process. Next, the Ni and Au layers 18 and19 are sequentially deposited on the Ru layer 17, so that the ohmicelectrode can be obtained.

Alternatively, an ohmic electrode having a condensed structure may beobtained by sequentially forming the contact metal (Me=Ir, Ni, Pt), Ag,Ru, Ni, and Au layers 15 to 19 and performing a thermal treatmentprocess on the resultant product under an oxygen atmosphere. After theohmic electrode is formed, a pattern for the ohmic electrode may beformed on the p-type GaN layer 14. In addition, the ohmic electrode maybe formed on the n-type nitride layer.

The gallium nitride-based III-V group compound semiconductor ispreferably at least one selected from a group of GaN, InGaN, AlGaN, andAlInGaN. The substrate is preferably one of a sapphire substrate, asilicon carbide (SiC) substrate, a silicon (Si) substrate, a zinc oxide(ZnO) substrate, a gallium arsenide (GaAs) substrate, and a galliumphosphate (GaP) substrate. The substrate is more preferably the sapphiresubstrate.

FIG. 2 is a graph showing current versus voltage of Me (=Ir, Ni,Pt)/Ag/Ru/Ni/Au p-type ohmic electrodes manufactured by performingthermal treatment processes for two minutes at a temperature of 500° C.under different atmospheres of oxygen and nitrogen. In comparison to thenitrogen-atmosphere thermal treatment process, the oxygen-atmospherethermal treatment process results in the ohmic property of the improvedcurrent-voltage properties.

FIG. 3 is a graph showing changes of contact resistivities of the Me(=Ir, Ni, Pt)/Ag/Ru/Ni/Au ohmic electrode according to the presentinvention and a conventional Ni(200?)/Au(1000?) ohmic electrode withrespect to oxygen-atmosphere thermal treatment temperature.

As shown in the figure, a low contact resistivity of 7×10−5 Ωcm² isobtained by performing a thermal treatment process at a temperature of500° C. It should be noted that, during a high temperature thermaltreatment process, the contact resistivity of the Me/Ag/Ru/Ni/Au ohmicelectrode relatively slowly increases, whereas the contact resistivityof the conventional Ni/Au electrode rapidly increases.

Accordingly, it can be understood that the multi-layered p-type ohmicelectrode according to the present invention has good thermal stability.

FIG. 4 is a graph showing reflectance of Me/Ag, Me/Ag/Ru, Me/Ag/Ru/Ni/Auohmic electrodes according to the present invention and the conventionalNi/Au p-type ohmic electrode with respect to wavelength of light. Asshown in the figure, at a wavelength of 470 mm, the reflectance of theMe/Ag and Me/Ag/Ru ohmic electrodes is 75%, but the reflectance of theMe/Ag/Ru/Ni/Au ohmic electrode is 90%, which is very high. In addition,it should be noted that the reflectance of the acnventional Ni/Au ohmicelectrode is 50%. Accordingly, it can be understood that theMe/Ag/Ru/Ni/Au p-type ohmic electrode according to the present inventionis very suitable for a high-reflectance electrode of a flip-chip LED.

FIG. 5 is a graph showing depth profiles of an Ir/Ag/Ru/Ni/Au ohmicelectrode manufactured by performing a thermal treatment process at atemperature of 500° C. for two minutes, wherein the depth profiles areobtained by using a secondary ion-mass spectroscopy (SIMS).

In comparison to the nitrogen-atmosphere thermal treatment process,external diffusion of Ga greatly increases by the oxygen-atmospherethermal treatment process. Therefore, it can be understood that a largernumber of Ga-vacancies are generated at an interface between GaN andmetal layers after the oxygen-atmosphere thermal treatment process. TheGa-vacancies serve as acceptors for generating holes, so that thecontact resistivity can be further lowered after the oxygen-atmospherethermal treatment process. Even though the nitrogen- andoxygen-atmosphere thermal treatment processes are performed, theexternal diffusion of Ag does not occur in a surface of the Ag layer.Therefore, it can be understood that the Ru layer serves as a diffusionbarrier layer for preventing external diffusion of Ag. In addition,after oxygen-atmosphere thermal treatment process, AgO is not generated.Therefore, it can be understood that the Ag layer performs its inherentrole as a reflective layer. Accordingly, it is possible to obtain highreflectance and good thermal stability by using the ohmic electrodeaccording to the present invention.

FIG. 6 is a graph showing operation voltage and light output of (300μm×300 μm) InGaN flip-chip LEDs manufactured by using an Me/Ag/Ru/Ni/Auohmic electrode according to the present invention and a conventionalNi/Au p-type ohmic electrode. For reference, a figure that schematicallyshows a method of measuring light outputs of the LEDs is inserted inFIG. 6. At an applied current of 20 mA, the operation voltage of the LEDdecreases from 3.73 V to 3.65 V, and the light output of the LED greatlyincreases from 16 a.u. to 31 a.u. Accordingly, in comparison to theconventional Ni/Au ohmic electrode, the high-reflectance Me/Ag/Ru/Ni/Auohmic electrode according to the present invention improves theproperties of the gallium nitride-based III-V group compoundsemiconductor LED device.

FIGS. 7 and 8 are graphs showing operation voltage and light output of(300 μm×300 μm) InGaN vertical-structure LEDs manufactured by using anMe/Ag/Ru/Ni/Au ohmic electrode according to the present invention and aconventional Ni/Au p-type ohmic electrode, respectively. In FIG. 7, across-sectional view of the vertical-structure LED is inserted. FIG. 9shows a photograph of the vertical-structure LED.

As shown in FIGS. 7 and 8, at an applied current of 20 mA, the operationvoltage of the LED using the high-reflectance Me/Ag/Ru/Ni/Au ohmicelectrode decreases by about 0.1 V, and the light output of the LEDincreases by about 30%.

According to the present invention, after an oxygen-atmosphere thermaltreatment process, an Me (=Ir, Ni, Pt)/Ag/Ru/Ni/Au ohmic electrodes haslow contact resistivity, high thermal stability, and a high reflectanceup to about 90%. By employing the Me/Ag/Ru/Ni/Au ohmic electrode, it ispossible to implement a gallium nitride-based III-V group compoundsemiconductor device having high reliability.

The scope of the present invention is not limited to the embodimentdescribed and illustrated above but is defined by the appended claims.It will be apparent that those skilled in the art can make variousmodifications and changes thereto within the scope of the inventiondefined by the claims. Therefore, the true scope of the presentinvention should be defined by the technical spirit of the appendedclaims.

INDUSTRIAL APPLICABILITY

As described above, the diffusion barrier layer is interposed betweenthe lower contact and reflective metal layers and the bonding metallayer, so that an ohmic electrode layer having low contact resistivityand improved reflectance can be obtained. In this case, the bondingmetal layer is formed after the contact and reflective metal layers areformed. However, if a predetermined thermal treatment process isperformed, the bonding metal layer is diffused into a lower layer, sothat the properties of the lower contact and reflective metal layers aredeteriorated. In order to solve the problem, the reflective metal layerand the diffusion barrier layer are sequentially formed, and then, anoxygen-atmosphere thermal treatment process is performed. As a result, alayer for protecting the lower metal layer can be obtained. That is, ina case where the diffusion barrier layer is made of Ru, the Ru isdeposited on the reflective metal layer, and the oxygen-atmospherethermal treatment process is performed, so that the Ru is oxidized intoRuO₂. As a result, it is possible to effectively protect the reflectivemetal layer.

1. A gallium nitride-based III-V group compound semiconductor devicecomprising: a gallium nitride-based semiconductor layer; and an ohmicelectrode layer formed on the gallium nitride-based semiconductor layer,wherein the ohmic electrode layer comprises a contact metal layer, areflective metal layer, and a diffusion barrier layer.
 2. Thesemiconductor device according to claim 1, wherein the ohmic electrodelayer further comprises at least one bonding metal layer.
 3. Thesemiconductor device according to claim 2, wherein the ohmic electrodelayer is formed by sequentially laminating the contact metal layer, thereflective metal layer, the diffusion barrier layer, and the bondingmetal layer.
 4. The semiconductor according to any one of claims 1 to 3,wherein the contact metal layer comprises at least one of Ni, Ir, Pt,Pd, Au, Ti, Ru, W, Ta, V, Co, Os, Re, and Rh.
 5. The semiconductoraccording to any one of claims 1 to 3, wherein the reflective metallayer comprises at least one of Al and Ag.
 6. The semiconductoraccording to any one of claims 1 to 3, wherein the diffusion barrierlayer comprises at least one of Ru, Ir, Re, Rh, Os, V, Ta, W, ITO(Indium Tin Oxide), IZO (Indium Zinc oxide), RuO₂, VO₂, MgO, IrO₂, ReO₂,RhO₂, OsO₂, Ta₂O₃, and WO₂.
 7. The semiconductor according to claim 2 or3, wherein the bonding metal layer comprises first and second bondingmetal layers, said first bonding metal layer comprising at least one ofNi, Cr, Ti, Pd, Ru, Ir, Rh, Re, Os, V, and Ta, said second bonding metallayer comprising at least one of Au, Pd, and Pt.
 8. A method ofmanufacturing a gallium nitride-based III-V group compound semiconductordevice, comprising steps of: forming a gallium nitride-basedsemiconductor layer having a PN contact structure on a substrate; andforming an ohmic electrode layer on the semiconductor layer, wherein theohmic electrode layer comprises a contact metal layer, a reflectivemetal layer, and a diffusion barrier layer.
 9. The method of accordingto claim 8, wherein the step of forming the ohmic electrode layercomprises steps of: sequentially laminating the contact metal layer, thereflective metal layer, and the diffusion barrier layer on thesemiconductor layer; performing a thermal treatment process; and forminga bonding metal layer on the diffusion barrier layer.
 10. The method ofaccording to claim 8, wherein the step of forming the ohmic electrodelayer comprises steps of: sequentially laminating the contact metallayer, the reflective metal layer, the diffusion barrier layer andbonding metal layer on the semiconductor layer; and performing a thermaltreatment process.
 11. The method of according to any one of claims 8 to10, wherein the thermal treatment process is a rapid thermal annealingprocess performed under an atmosphere of 5 to 100% oxygen at atemperature of 100 to 700° C. for 10 to 100 seconds.